A useful metric to compare the performance of quantum memories is the ratio of the noise counts on the output to the total memory efficiency: \(\mu _1 = N/\eta _\textrm {mem}\)  [1]}. This parameter \(\mu _1\)  is essentially the number of photons per pulse on average at the input of the quantum memory that gives an SNR = 1 at the output. For the data in Fig. REF  we measure the noise to be \(N = 9(1) \times 10^{-7}\)  photons per pulse over the integration window of \(500\,\) ps. This leads to \(\mu _1\)  = \(4.5(6)\times 10^{-6}\)  which is approximately one order of magnitude improvement compared to the previous ORCA demonstrations [2]}, [3]}, [4]}, and to our knowledge the lowest reported for atom-based quantum memories.
<FIGURE>